The invention concerns a method for automatically controlling an internal combustion engine, where, during normal operation in a first controller mode, a charge air temperature controller is set as dominant for a map-controlled thermostatic valve for automatically controlling the charge air temperature, or, during normal operation in a second controller mode, a coolant temperature limit controller is set as dominant for the map-controlled thermostatic valve for automatically controlling the coolant temperature, where if a charge air temperature sensor fails, the second controller mode is set with the coolant temperature limit controller dominant, and where if a coolant temperature sensor fails, the first controller mode is set with the charge air temperature controller dominant.
A cooling circulation system of an internal combustion engine is known from the journal Schiff & Hafen/Kommandobrücke, No. 1, 1990, pp. 49-50. The cooling circulation consists of a high-temperature circulation with a coolant pump and a low-temperature circulation that branches off from the high-temperature circulation. In the low-temperature circulation, a thermostatic valve, a recooler with a bypass line, a charge air cooler, and a lubricating oil heat exchanger are arranged in series. The coolant flow in the low-temperature circulation diverted from the high-temperature circulation is divided by the position of the thermostatic valve into a recooler coolant flow, which flows through the recooler, and a bypass coolant flow. Downstream of the recooler, the two coolant flows are brought together again and fed to the charge air cooler as the charge air cooler coolant flow. The thermostatic valve thus determines the temperature of the charge air cooler coolant flow via the distribution of the coolant flow. The temperature of the charge air cooler coolant flow in turn defines, via the temperature difference from the charge air temperature, the amount of heat extracted from the charge air in the charge air cooler. For example, when the internal combustion engine is under full load, the thermostatic valve is completely open, so that the entire coolant flow of the low-temperature circulation flows through the recooler, and therefore the greatest possible amount of thermal energy is extracted from the charge air. By contrast, when the internal combustion engine is idling, the thermostatic valve is completely closed, so that the entire coolant flow of the low-temperature circulation flows through the bypass line, and very little thermal energy is extracted from the charge air. The switching state of the thermostatic valve is determined by a thermostatic operating element, for example, an expanding material element, which expands with increasing temperature of the coolant flow, so that the thermostatic valve opens, or contracts with decreasing temperature of the coolant flow, so that the thermostatic valve closes under spring tension. Due to the design of the thermostatic valve, automatic control of the charge air temperature is still not possible at all operating points.
DE 201 22 420 U1 discloses an electrically heated thermostatic valve in which the characteristic curve of the thermostatic operating element can be shifted by the electric control of the heating element. For example, when an internal combustion engine is cold, and a large load is demanded, the coolant flow can be influenced by the bypass line at an earlier time than would be possible by the thermostatic operating element. In the remainder of the text, a thermostatic valve of this type will be referred to as a map-controlled thermostatic valve. DE 102 23 686 A1 discloses a corresponding method for controlling this map-controlled thermostatic valve. It describes two-position control with input control of the operating element. However, this method does not offer significant improvement with respect to the automatic control of the charge air temperature in the coolant circulation described above.
The unprepublished German patent application with the official file number DE 10 2007 056 360.6 describes a method for automatically controlling the charge air temperature or the coolant temperature by a map-controlled thermostatic valve in the cooling circulation system described above. In a first controller mode, a charge air temperature controller is set as dominant for the map-controlled thermostatic valve to automatically control the charge air temperature. In a second controller mode, a coolant temperature limit controller is set as dominant for the map-controlled thermostatic valve to automatically control the coolant temperature. Under normal operating conditions, the charge air temperature is determined over the entire operating range of the internal combustion engine by the charge air temperature controller. However, if the coolant temperature rises to an impermissible level, the coolant temperature limit controller becomes dominant. Basically, the controller which would be able to provide stronger cooling is the one which is set as dominant for the map-controlled thermostatic valve. Measures to be taken in the event of a sensor failure, for example, the charge air temperature sensor and/or the coolant temperature sensor, are not indicated in the cited document.
DE 100 32 110 A1 discloses a diagnostic function for a closed-loop control structure with a speed controller and a torque limiter, which act on the same actuator. However, the diagnostic function considers only the case of the occurrence of an error in the torque determination. Practically speaking, in this method, during normal operation, either the speed controller or the torque limiter is set as dominant for a power-determining signal, for example, an injection quantity. If the diagnostic function detects an error in the torque determination, then, if the speed controller is dominant, it remains dominant. If, on the other hand, the torque limiter is dominant, dominance then passes to the speed controller. The cited document fails to describe what procedure is followed if an error occurs in the speed determination.